1. Field of the Invention
The present invention relates to a method of producing a photoresist, more particularly, to a method of producing a photoresist suitable for lithography acting by a radiation such as ultraviolet ray, far ultraviolet ray, electron beam, X ray and the like.
2. Prior Art
Photoresists have been produced by mixing and dissolving resist constituent components such as a sensitizing agent, alkali-soluble resin, acid generator, quencher and the like into a resist solvent, and filtrating the resulted raw resist solution through a filter made of at least one resin selected from fluorine-based resins and polyolefins, to remove fine particles in the solution.
However, the above-mentioned filter, when used for a filtration operation repeatedly, causes clogging by fine particle arrested on the filter, and further use thereof becomes difficult. Consequently, there is a problem that the filter must be changed frequently, increasing production cost.
The present inventors have intensively studied to solve this problem, and resultantly found that the above-mentioned problem can be solved by washing a filter used once or more times for filtration of a raw resist solution, with a solvent containing the resist solvent, toward the reverse direction to the filtration direction, and filtrating the raw resist solution using this washed filter.
The present inventors have found that a filter used once or more times for filtration of a raw resist solution and washed with a solvent containing the resist solvent toward the reverse direction to the filtration direction can be used also for filtration of an alkali-soluble resin solution. They have also found that further decrease in production cost can be attained by producing a photoresist using thus obtained alkali-soluble resin solution.
Further, conventionally, when, after production of a photoresist, the same or different kind of photoresist is produced subsequently using the same production apparatus, even if a resist solvent for the photoresist in the former production and a resist solvent for the photoresist in the latter production are the same, it is necessary to sufficiently wash the production apparatus after production of the photoresist in the former production and before production of the photoresist in the latter production. If this washing is insufficient, various problems occur such as increase by time in the number of particles in the resist solution, deterioration in lithography ability, and the like.
Particularly, in the case of sequential production of two or more photoresists having mutually different resist constituent components using the same production apparatus, if washing thereof is insufficient, a problem occurs that resist constituent components of a photoresist in the former production are mixed into a photoresist in the subsequent production. Accordingly, respective photoresists are often produced by using different production apparatuses, in such a case. According to this method, however, it is required to provide a lot of production apparatuses for producing many articles of photoresists, being unsatisfactory from the standpoint of production efficiency.
The present inventors have further found that if, in a method of sequentially producing two or more photoresists having mutually the same or different resist constituent components and using mutually the same resist solvent by using the same production apparatuses, this production apparatus is washed with the resist solvent, a solvent other than this resist solvent capable of dissolving or decomposing the resist constituent components, and the resist solvent, in this order, after production of the photoresist and before production of the subsequent photoresist, sufficient washing can be attained and the problem in the case of sequential production using the same production apparatus can be solved.
The present invention has been completed based on these findings.